A solid-state image pickup apparatus (camera module) which is applied to a camera of a mobile phone is normally arranged such that a solid-state image sensing device, a digital signal processing device (DSP), a lens, a lens holder, and a camera cone are integrated in a package. Mainly, conventional solid-state image pickup apparatuses are of single-focus type. On the other hand, a solid-state image pickup apparatus has been required, in recent years, to have higher pixel density, higher image quality, and higher function. For this reason, even a solid-state image pickup apparatus which is incorporated in a mobile phone is equivalent with a dedicated image pickup device, such as a digital still camera in terms of the number of pixels. Furthermore, such a solid-state image pickup apparatus is loaded with an optical system for realizing a zooming function or an automatic focusing function.
On the other hand, in order to cause a solid-state image pickup apparatus to function as designed, it is necessary to cause an optical center of a solid-state image sensing device to coincide with an optical center of optical components, including a lens. The optical center of the solid-state image sensing device is a design center of a pixel plane which is formed by a plurality of pixels provided on the solid-state image sensing device, that is, a pixel center. On the other hand, the optical center of the optical components is a center of the lens, that is, an optical axis. When the pixel center and the center of the lens (optical axis) do not coincide with each other, there occurs a problem that four corners of a picked-up image blur or darken due to the design of the solid-state image sensing device.
Accordingly, in order to cause a solid-state image pickup apparatus to have higher pixel density, higher image quality, and higher function, it is essential (i) that the pixel center and the optical axis be collinearly provided and (ii) that a light receiving plane (light receiving surface) of the solid-state image sensing device and the optical axis intersect at right angles.
In an early stage where a solid-state image pickup apparatus became incorporated in a portable device or a mobile phone, the solid-state image pickup apparatus was extremely simply and easily arranged from the viewpoint of miniaturization and weight reduction. On the contrary, a recent solid-state image pickup apparatus has been arranged such that a precise and highly accurate system is applied and a light receiving section of the solid-state image sensing device becomes finer in accordance with a development in the process of producing an IC. Against this backdrop, a higher accuracy is required in positionally aligning the pixel center and the center of the lens when a solid-state image pickup apparatus is assembled.
On the other hand, a portable device or a mobile phone in which a solid-state image pickup apparatus is incorporated is required to be miniaturized (downsized), lighter, and power-saved. This makes it impossible to apply, to a solid-state image pickup apparatus which is incorporated in a portable device or a mobile phone, a complicated correction system which is employed for a general dedicated image pickup device so as to correct positioning of the pixel center and the center of the lens.
Conventionally, positioning of optical components at the time of assembly of a solid-state image pickup apparatus has been carried out with reference to a wiring substrate on which the solid-state image sensing device is mounted. Specifically, the positioning is carried out in such a manner that: the light receiving surface of the solid-state image sensing device is regarded as identical or parallel to a mounted surface of the wiring substrate on which mounted surface the solid-state image sensing device is mounted; and optical components, such as a lens and a lens holder are positioned with reference to the mounted surface so as to be mounted on the wiring substrate.
For such positional alignment of optical components, it is possible to use a device for mounting a component on a wiring substrate (soldering device). This brings about an advantage that it is possible to reduce capital investment to the minimum and to employ know-how as well. However, as a recent solid-state image pickup apparatus becomes more accurate, revealed are: (i) variations in production of a wiring substrate, (ii) variations in sizes of components to be loaded in a solid-state image pickup apparatus other than the optical components, or (iii) variations in an accuracy in assembly or mounting of the components.
It is possible to carry out focus (focal length) adjustment by devising various methods after a solid-state image pickup apparatus is assembled. However, an uneven blur in an image (a state in which an image is unevenly focused between top and bottom or between left and right) or a state in which four corners of an image darken is due to the positioning of optical components at the time of assembly of a solid-state image pickup apparatus. This makes it impossible to correct the focus by fine adjustment after the solid-state image pickup apparatus has been assembled. Accordingly, it is extremely important how accurately optical components are positioned when a solid-image pickup apparatus is assembled.
Therefore, Patent Literatures 1 through 3, for example, disclose respective methods for positioning such optical components.
FIG. 11 is a schematic view illustrating the positioning method described in Patent Literature 1. Patent Literature 1 discloses a surface mounting technology in which a component is mounted on a printed circuit board. In Patent Literature 1, a specific positioning mark (alignment mark) is provided on a printed circuit board so as to mount a component on the printed circuit board. A component is loaded in a desired position according to calculation by use of this positioning mark and design information.
Specifically, a pattern or hole 202 which has a specific shape and is provided on a printed circuit board is recognized as a reference position (see FIG. 11). A mounted position (P) on which a component 203 is mounted is predetermined, and it is thus possible to calculate a positional relationship between the reference position and the component 203 by use of design information (e.g., a size, coordinate information or the like of CAD data). For this reason, in a case where the component 203 is provided in a position (P0) on the printed circuit board which position is shifted from the mounted position, the position of the component 203 is corrected so as to have the positional relationship between the reference position and the component 203 which positional relationship is calculated by use of the design information. This allows the component 203 to be provided and mounted in a given position on the printed circuit board.
FIG. 12 is a cross-sectional view illustrating a solid-state image pickup apparatus described in Patent Literature 2. A solid-state image pickup apparatus 300 is arranged such that notches which are formed in a leg portion 303 of a lens section 302 fit to four corners of a solid-state image sensing device 301. This allows the leg portions 303 to be directly brought into contact with a light receiving surface of the solid-state image sensing device 301, so that the lens section 302 is positioned.
FIG. 13 is a cross-sectional view illustrating a solid-state image pickup apparatus described in Patent Literature 3. A solid-state image pickup apparatus 400 is arranged such that a bottom of a lens holder 404 is brought into contact with a transparent cover section 402 which is adhered to a solid-state image sensing device 401 and which is exposed in a sealing section 403 (see FIG. 13). This allows a lens 405 to be positioned in consideration of the solid-state image sensing device 401.
However, a conventional solid-state image pickup apparatus has problems of: (i) positioning of optical components with low accuracy and (ii) vulnerability to an external shock.
Specifically, application of the method described in Patent Literature 1 for soldering a component onto a printed circuit board to production of a solid-state image pickup apparatus causes a reference for positioning optical components to be provided on a printed circuit board. Namely, the reference point on the printed circuit board indirectly positions the pixel center of the solid-state image sensing device and the optical axes of the optical components. However, according to this method, (i) variations in production of a printed circuit board, (ii) variations in sizes of components provided on the printed circuit board other than the optical components, (iii) variations in an accuracy in mounting (assembly) of the components on the printed circuit board, or (iv) the like are adversely added to an accuracy in positioning of the optical components. This produces an error in the positioning of the optical components, and it is thus impossible to position the optical components with high accuracy.
Furthermore, it is also possible to provide the reference for positioning the optical components on the solid-image sensing device (an LSI) when the method of Patent Literature 1 is applied to the production of a solid-state image pickup apparatus. However, it is virtually impossible to provide a positioning reference, such as a size, a color, or a contrast which can be recognized by an apparatus (actually a camera capable of taking a close-up) for recognizing the reference for positioning the optical components.
Moreover, the solid-state image pickup apparatus 300 of Patent Literature 2 is arranged such that the leg portion 303 of the lens section 302 is directly brought into contact with the solid-state image sensing device 301, so that optical components are positioned (see FIG. 12). For this reason, when this solid-state image pickup apparatus 300 is incorporated in a portable device, a shock due to falling or the like is transmitted directly to the solid-state image sensing device. This causes displacement of the solid-state image sensing device 301.
Further, a short-circuit which occurs between a power source and an earth (a ground) due to a crack made in the solid-state image sensing device 301 by a shock may generate heat in a device (battery section).
Furthermore, the solid-state image pickup apparatus 400 of Patent Literature 3 is arranged such that the bottom of the lens holder 404 is brought into contact with the transparent cover section 402. This causes a shock to the solid-state image pickup apparatus 400 to be transmitted to the solid-state image sensing device 401 through the transparent cover section 402. As a result, displacement or breakage of the solid-state image sensing device 401 may occur similarly to the case of the solid-state image pickup apparatus 300 of Patent Literature 2. Moreover, the transparent cover section 402, which is normally made of a glass substrate, is weaker in mechanical strength or more vulnerable than a wiring substrate on which the solid-state image sensing device 401 is provided. For this reason, when a shock is applied directly to the transparent cover section 402, the transparent cover section 402 is easy to break and the solid-state image pickup apparatus 400 is easy to malfunction.
Moreover, the solid-state image pickup apparatus 400 of Patent Literature 3 is arranged such that: a bottom surface of the lens holder 404 is brought into contact with a top surface of the transparent cover section 402 and a positioning claw 408 abuts on a peripheral side section of the transparent cover section 402; and a claw section 407 formed in the sealing section 403 is fit to a supporting section 406. This fixes a relative position of the transparent cover section 402 and the lens holder 404.
The solid-state image pickup apparatus 400 is actually arranged such that a part in which the positioning claw 408 abuts on the transparent cover section 402 and a part in which the claw section 407 is fit to the supporting section 406 are provided to have some space (play). However, a solid-state image pickup apparatus is required to be miniaturized (downsized) as described earlier, and it is thus impossible to allow even room for formation of such space (play). Furthermore, only when there is room in design, it is possible to form a member, such as the claw section 407 which is formed in the sealing section 403. However, neither the claw section 407 nor the part to which the claw section is fit is not what fulfills a primary function of the solid-state image pickup apparatus 400. As described earlier, the arrangement in which the optical components are positioned in the solid-state image pickup apparatus 400 of Patent Literature 3 is contrary to a requirement for miniaturization (downsizing). Accordingly, such an arrangement should be excluded as much as possible, and miniaturization should be promoted, instead.
Citation List
Patent Literature 1
Japanese Patent Application Publication, Tokukaisho, No. 61-19200 A (Publication Date: Jan. 28, 1986)
Patent Literature 2
Japanese Patent Application Publication, Tokukai, No. 2003-338964 A (Publication Date: Nov. 28, 2003)
Patent Literature 3
Japanese Patent Application Publication, Tokukai, No. 2006-279533 A (Publication Date: Oct. 12, 2006)